Known converter circuits comprise a multiplicity of actuatable power semiconductor switches which are connected in a known manner in order to switch at least two switching voltage levels. Typically, a converter circuit of this kind is connected to an electrical AC mains system of, in particular, three-phase design. Such converter circuits are frequently used in industrial installations, wherein the converter circuits are coupled to the mains and wherein further fields of use and opportunities for use are naturally conceivable.
For operation of the converter circuit, a control apparatus is provided which has a control unit for forming a control signal by adjusting an H-th harmonic component of system currents to a system current setpoint value and which is connected to the actuatable power semiconductor switches via an actuation circuit for forming an actuation signal from the control signal, wherein the H-th harmonic component is produced by the converter circuit and generally H=1, 2, 3, . . . . Typical values of H are H=−5, 7, −11, 13. The actuation signal is therefore used to actuate the power semiconductor switches.
The above method for operating the converter circuit allows the control apparatus to be used to adjust an H-th harmonic component of the system currents to a system current setpoint value. However, besides harmonic components in the system currents, harmonic components in the system voltages may also arise in an electrical AC mains system, but these cannot be adjusted using the known method described above and therefore cannot be reduced.